1. Field of the Invention
This invention relates generally to electromagnetic switching devices and more particularly to an improved magnetic latching reed delay.
2. Description of the Prior Art
For many years the mainstay of switching and logic circuits has been, the well-known electromechanical relay. The relay consists of a magnetic flux-producing coil of wire and at least one contact pair operable in response to the generation of the magnetic flux. In order to achieve the operational speeds necessary to make relays compatible with transistor circuitry, a special type of relay, called the reed relay, has been designed. Reed relays usually have a pair of make contacts or reed blades placed within a glass-enclosed capsule with a control winding placed around the capsule.
Numerous improvements have been made to such reed relays to improve their time-response characteristics and to provide for self-holding capability. For example, a current pulse through the control winding causes the relay to operate and remain operated until a second currect pulse is applied. One such type of self-holding relay has contacts made from a magnetic material which, when exposed to a magnetic flux, will assume a magnetic state and will remain in that state until exposed to a magnetic flux of an opposite direction. These relays are normally called remanent reed relays. An example of such a relay is taught by U.S. Pat. No. 3,059,075 issued to R. L. Peek on Oct. 16, 1962.
Various arrangements of control windings have been employed with magnetic latching reed relays. One such arrangement is taught by U.S. Pat. No. 3,037,085 issued to T. N. Lowry on May 29, 1962. This arrangement employs a principle of differential excitation and uses two pairs of windings connected so that the relay is released, i.e., the contact pair is opened, by applying a current pulse to one pair of windings. The relay is operated, i.e., the contact pair is closed, by concurrently applying pulses of the same polarity to both pairs of windings. A problem existing with the differential excitation arrangement, is that the current pulse which operates the relay (closes the contact pair) must, be a dual pulse applyied to both windings concurrently. This results from the fact that, the application of current to a single winding of the relay causes the relay to release. Thus, from a circuit design standpoint, provisions must be made for supplying two simultaneous pulses of current. In certain applications, such as in selectable matrix arrays, it may be desirable to operate a relay only upon coincidence of pulses, in logic circuitry such a result is difficult and costly to achieve.
Another control winding arrangement is taught by U.S. Pat. No. 3,793,601 issued to R. J. Anger et al on Feb. 19, 1974. This arrangement operates or releases the reeds with a single pulse. Each of a pair of identical release windings is arranged over a corresponding one of a pair of reeds. The release windings are series connected so that a single pulse applied to the windings causes a magnetic field of one direction to be produced around one reed and a magnetic field of an opposite direction to be produced on the other reed. The resultant magnetic flux is such that the contact ends of the reeds are of the same magnetic polarity and thus separate. An operate winding in association with one of the two release windings is wound in a manner as to produce a magnetic flux magnitude greater than the magnetic flux magnitude generated by the associated release winding and having a flux direction opposite to the flux direction produced by the associated release winding. The operate winding is series connected to the associated winding, so that, a single current pulse flowing through the operate and the pair of release windings causes the contact ends of the reeds to have magnetic states of opposite polarity, with the result that the contact ends of the reeds attract, closing the contact pair. Such arrangement is costly requiring at least three separate and distinct windings, adds unwanted weight and bulk to the relay, and increases the assembly time.
Accordingly, it is an object of the present invention to provide a single coil self-holding remanent reed relay capable of single-pulse selective operation.